Variable Valve Timing Pushrod Motor

Ron Earp · 10-14-07, 07:53 AM

I saw an interesting piece in a magazine some years ago about a GM test mule pushrod engine with two cams in the block. Idea was to offer some variable valve timing but I never saw anything else about that design.

I recently read a small tech brief about the new Dodge Viper variable cam timing setup that was developed by Mahle. Looks really need with a solid cam inside a hollow cam so that the exhaust valve timing can be adjusted. A short SAE piece can be found here:

SAE Variable Viper Timing

Interesting technology. It'll be really neat if we see aftermarket kits to retrofit to old style pushrod motors but I imagine there would be a myriad of obstacles. There is mention of GM coming out with a variable valve timing system for their pushrod V8s. Again, Ford is left out as they don't even have a push rod program, instead banking everything on the complex, large, and expensive modular motors.

Ron

Richard B. · 10-14-07, 08:44 AM

Personally I think continuing to work with variable cam timing with camshafts is a waste of time. With the advances in technology and electronics they need to work on developing and engine with valves operated by solenoids. With this type of setup, untold amounts of horsepower could be freed up since you will no longer be spinning a camshaft moving all the lifters and valves. Not only wopuld the valve timing be infinitely adjustable, but the opening duration could also be tailored to the rpm and engine output.

Ron Earp · 10-14-07, 08:58 AM

The solenoid setup is truly the best solution I think. Eliminates the throttle and other complexities as well.

The last I read of solenoid technology (some years ago) being used on a motor was a test mule at a university. The motor was limited to about 4000 RPM at which point the solenoid could not maintain opening control of the valve. As I recall field limitations for the electromagnet and current draw were cited as part of the limiting issues. But, if we get some room temperature (and higher for engine op temps) superconductors those issues will disappear in a hurry! With even a 3000 RPM limit though it could be useful for diesels, if it could control a valve large enough and the MTBF is long enough to use on an engine.

I did a quick search and turned up quite a few patents on solenoid valve actuation but no summaries involving current state of the art.

Paul · 10-14-07, 12:51 PM

Formula one's use hydraulic fluid to open and close their valves which allows them to reach the 19000rpm ranges. The big problem with solenoids is the residual currents generated by the magnetic fields building up and decaying in the coils.

Jac Mac · 10-14-07, 04:17 PM

Its high time we got out of the need for valves altogether and went to fourstroke ported engines which dont have pistons as we know them anyway!

Jac Mac

BruceLambo · 10-14-07, 05:07 PM

Well interesting you should bring this up. I had been buggering around with such things a few years ago, but suitable equipment and understanding put the idea in the trash can. I though about the almost same idea as that of the, now-in-use vvt cam in block idea.
Check out this site, it shows you exactly how it works. Engine Variable Valve Timing | VVT | Concentric Camshafts | Cam In Block Engines.
As well as being part of the new Viper, VVT for our beloved V8s with cam-in-block is a production reality for the new Chevy Vortec L76 engine. It is the Generation 4 smallbock 6litre jobby. The other one it is in, is the new Cadillac. Its an all alloy engine 6.2 litre, push rod engine with VVT.

Alex · 10-15-07, 01:17 AM

it's pretty simple to put variable cam timing on a pushrod engine. put an actuator on the timing belt/chain tensioner to push/pull the chain. have a 2nd tensioner to take up the slack, and a computer to control the actuator. you have variable cam timing (in relation to the crank), and thus variable valve timing.

BruceLambo · 10-15-07, 04:05 AM

Quote:

Originally Posted by alex427LS1

it's pretty simple to put variable cam timing on a pushrod engine. put an actuator on the timing belt/chain tensioner to push/pull the chain. have a 2nd tensioner to take up the slack, and a computer to control the actuator. you have variable cam timing (in relation to the crank), and thus variable valve timing.

Yep, thats how the new Porsches do it with their VarioCam system. The thing is with the cam-in-block system as used above, is it gives continuously independant, variable cam timing on both intake and exaust.

Scott Calabro · 10-15-07, 08:17 AM

Hey Jac Mac!

You mean something like what Hugo Junkers came up with .....

http://www.enginehistory.org/Diesels/CH4.pdf

Or perhaps this .....

Gemini 100 - September 2007 Issue - (Aircraft Maintenance Technology)

S

speed220mph · 10-15-07, 09:05 AM

Variable cam timing has huge benefits in power, economy and driveability . . . and it's becoming commonplace just like variable spark advance. Everyone knows you advance cams for low-end torque and retard them for high-end power, which is especially important on the street. This is now commonly done with hydraulic actuators between the cam-drive sprockets and cam. Yes, there have been growing problems, but that's the way all advancements have been. (Good things the Wright Bros. didn't give up.LOL) And it can be done with pushrod engines, too, but when you're tight on resources,aka bucks, Ford is concentrating on OHC engines and not the aftermarket pushrod engines.

As for F1 cars and their hydraulically acuated valves, springs alone can't handle opening and closing the valves over 150 times a second at current engine speeds. But this is not required on the typical street engine. Even with pushrod race engines valves are operating at around 80 times a second and piston speeds equal or exceed those of F1 engines. Things get a bit complex, but it boils down to budgets. A lot of things are possible, but not feasible unless you're using tax-payer money or have an F1 budget, whichever is higher.

Another great development has been the dual intake ports with butterflies in one runner. Again, this is to maintain port velocities at the high and low ends of engine speeds. So when the technology is available to give us fuel injection . . . direct, no less . . . electronic spark timing and variable compression (some day), it would be foolish not to use it. Who woulda' thunk that a 7.0L engine even without variable cam timing could produce over 500 hp and get 27 mpg on the highway? As for now the Holley carbs on the engines in my toys and hi-tech engines in the tow truck and family rides make a great combination.

Jac Mac · 10-15-07, 03:04 PM

Quote:

Originally Posted by 5150

Hey Jac Mac!

You mean something like what Hugo Junkers came up with .....

http://www.enginehistory.org/Diesels/CH4.pdf

Or perhaps this .....

Gemini 100 - September 2007 Issue - (Aircraft Maintenance Technology)

S

No Scott,
But for the sake of the LSA movement I hope the GEMINI project gets off the ground and is not killed off by all the existing scaredy cats in aviation .

Jac Mac

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